Minimally invasive spinal surgery, which avoids long incisions and attendant muscle damage, blood loss, and scaring associated with convention spinal surgery, is also credited with shortening recovery periods and reducing postoperative pain, while producing good long-term outcome. Access portals to surgical sites are formed by making short incisions (e.g., less than two centimeters) followed by progressively dilating and retracting intervening tissue. Traditional spinal surgical procedures such as spinal fusion, disc repair, and deformity corrections can be performed through the access portals, which are also referred to as working channels.
Typically, a set of dilators is used to form the access portals, beginning with a guide wire or pin that is inserted through the small incision and advanced until the wire contacts bone in the vicinity of the intended surgical site. Progressively larger tubular dilators are inserted over the guide wire or pin in sequence for stretching muscle and other intervening tissue. A circular retractor replaces the final dilator for holding back the stretched muscle and maintaining a working channel that exposes the intended surgical site. A linkage assembly attached to the surgical table can be used for holding the retractor in place. Surgical tools are inserted through the working channel within the retractor to perform the desired operation. Generally, the surgical site can be viewed directly through the circular retractor. However, an endoscope can be inserted into the working channel to provide enlarged imaging from one or more local perspectives of the surgical site.
US Patent Application Publication 2005/0101985 to Hamada discloses a tapered obturator for replacing the conventional series of dilators. The tapered obturator spreads tissue, first by working its tapered nose to depth and then by temporarily pivoting hemispheric sections apart. After re-closing the hemispheric sections of the obturator, a working tube, which also has hollow hinged hemispheric sections, is inserted over the obturator to secure the dilation gains. The obturator is then re-opened to pivot apart the hollow hemispheric sections of the working tube, further spreading tissue near the surgical site. Lock pins hold the hemispheric sections of the working tube apart, while the obturator is withdrawn to expose a working channel that expands in one dimension approaching the surgical site.
US Patent Application Publication 2004/0230100 to Shluzas discloses a retractor having a wrap-around skirt for similarly expanding a working channel approaching a surgical site. The retractor, while in a generally cylindrical configuration, is inserted over a dilator or dilator assembly that initially reaches the surgical site. The dilator or dilator assembly is then removed to provide access for inserting a scissored expander, which unfurls the wrap-around skirt into a generally conical form. The scissored expander is then removed to expose the surgical site through the expanded retractor.
U.S. Pat. No. 6,206,826 to Matthews et al. discloses a retractor ring formed by concentric inner and outer walls that are partitioned into channels or other openings for holding or guiding surgical tools and ancillary instrumentation. Retractor blades attach by way of clips to the outer wall of the ring. A circular sleeve fits within the inner wall of the ring to provide general surgical access. In between, the partitioned channels of the ring receive ancillary instruments in support of surgical operations. The ring functions as a surgical organizer for arranging surgical instruments within a small access portal and for training surgeons otherwise unaccustomed to working through small working channels to surgical sites.
Conventional retractors, the hinged retractor of Hamada, the wrap-around retractor of Shluzas, and the retractor ring assembly of Matthews et al. maintain fixed access portals to surgical sites. Adjustments to the size or shape of the portals require the participation of additional dilators, obturators, or expanders, which block the working channel until the adjustments are complete. Any change to the size or shape of the portal entrance requires a different retractor or retractor ring.
Other minimally invasive access systems have evolved closer to conventional surgical retractor systems but on a smaller scale. For example, U.S. Pat. No. 5,944,658 to Koros et al. discloses a retractor and distractor system that mounts a set of retractor/distractor blades from an adjustable frame. Two arms of a retractor frame suspend opposing retractor blades. A crossbar linkage between the two arms of the retractor frame includes a gear rack drive for adjusting the spacing between the retractor blades. Two arms of a distractor frame suspend opposing distractor blades at right angles to the two arms of the retractor frame. A similar crossbar linkage between the two arms of the distractor frame adjusts the spacing between the distractor blades. A tilting structure is also provided for pivoting the retractor bales together with their support arms about the remaining retractor frame. Despite the complexity of the frame-based system, the manipulation of individual blades is limited, while the entire system can be unwieldy for use securing the small surgical portals required for conducting minimally invasive surgery.